An in-vehicle navigation device mounted in a vehicle retrieves an optimum route to a destination by using map data and guides the vehicle along the optimum route. In the map data, a road is expressed by links that are connected via nodes. The navigation device computes, with respect to each link and each node, a cost that indicates easiness in passing, and retrieves a route whose total cost of constituting links and nodes is minimum among routes from a starting position to a destination by the Dijkstra method.
However, thus retrieved route is not always preferable to users. A user may prefer to driving a road that is narrower but shorter, or to driving a road that is more detouring but less traffic. In this case, the preferred road may not correspond to the low cost road. Furthermore, a preferred road may be excluded from roads used for route retrieval because of being too narrow or one-way traffic. In this case, the preferred road is never retrieved as a part of the optimum route.
To solve this problem, a navigation device in Patent Document 1 is provided with the following. When a subject vehicle travels a certain route (referred to as a deviation route) different from an initially retrieved route, the deviation route is stored along with its deviating position from the retrieved route and its returning position to the retrieved route. When the deviating position and the returning position are thereafter included in a retrieved route, a part of the route therebetween can be replaced with the deviation route that was previously traveled. In other words, the deviation route is treated as a route preferred by a user, so the deviation route can be included in a guiding route.
However, the deviation route is not always a preferred route even when a user takes the deviation route. For instance, a deviation route might be reluctantly taken or traveled because of road traffic closure or road repairing. Furthermore, in this case, a route corresponding to the road traffic closure can be bypassed from any one of multiple deviating position candidates to any one of multiple returning position candidates.
Here, in Patent Document 1, when both the deviating position and the returning position previously stored are included within a retrieved route that is thereafter newly retrieved, the impassable route can be prevented from being selected. However, when both the deviating position and the returning position previously stored are not included within a retrieved route, this retrieved route is selected without any specific replacement. Namely, for instance, when a retrieved route that is thereafter retrieved includes the same road traffic closure but does not include the previously traveled returning position to the previous initially retrieved route, this retrieved route is used for route guidance without any replacement although it includes the same road traffic closure that the vehicle previously bypassed.
Furthermore, it can be designed that information regarding the road traffic closure or road repairing is received via the VICS (Vehicle Information and Communication System) or the like and a route detouring around the impassable route is retrieved based on the received information. However, the VICS provides information mainly related to major roads, so roads other than the major roads cannot be included in the VICS information.                Patent Document 1: JP-2001-124578 A (U.S. Pat. No. 6,418,373 B1)        